[PATCH 2/3] userfaultfd: non-cooperative: generalize wake key structure

[Mike Rapoport]

Upcoming support for synchronous non-page-fault events will require
userfaultfd_wake_function to be able to differentiate between the event
types. Depending on the event type, different parameters will define if the
wait queue element should be awaken. This requires more general structure
than userfaultfd_wake_range to be used as the "key" parameter for
userfaultfd_wake_function.
This patch introduces userfaultfd_wake_key that is used for waking up
threads waiting on page-fault and non-cooperative events.

Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
---
 fs/userfaultfd.c | 114 +++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 72 insertions(+), 42 deletions(-)

diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index b32c7aaeca6b..d9f74b389706 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -91,21 +91,44 @@ struct userfaultfd_wake_range {
 	unsigned long len;
 };
 
+struct userfaultfd_wake_key {
+	u8 event;
+	union {
+		struct userfaultfd_wake_range range;
+	} arg;
+};
+
+static bool userfaultfd_should_wake(struct userfaultfd_wait_queue *uwq,
+				    struct userfaultfd_wake_key *key)
+{
+	/* key->event == 0 means wake all */
+	if (key->event && key->event != uwq->msg.event)
+		return false;
+
+	if (key->event == UFFD_EVENT_PAGEFAULT) {
+		unsigned long start, len, address;
+
+		/* len == 0 means wake all threads waiting on page fault */
+		address = uwq->msg.arg.pagefault.address;
+		start = key->arg.range.start;
+		len = key->arg.range.len;
+		if (len && (start > address || start + len <= address))
+			return false;
+	}
+
+	return true;
+}
+
 static int userfaultfd_wake_function(wait_queue_entry_t *wq, unsigned mode,
-				     int wake_flags, void *key)
+				     int wake_flags, void *_key)
 {
-	struct userfaultfd_wake_range *range = key;
+	struct userfaultfd_wake_key *key = _key;
 	int ret;
 	struct userfaultfd_wait_queue *uwq;
-	unsigned long start, len;
 
 	uwq = container_of(wq, struct userfaultfd_wait_queue, wq);
 	ret = 0;
-	/* len == 0 means wake all */
-	start = range->start;
-	len = range->len;
-	if (len && (start > uwq->msg.arg.pagefault.address ||
-		    start + len <= uwq->msg.arg.pagefault.address))
+	if (!userfaultfd_should_wake(uwq, key))
 		goto out;
 	WRITE_ONCE(uwq->waken, true);
 	/*
@@ -585,7 +608,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 		goto out;
 
 	ewq->ctx = ctx;
-	init_waitqueue_entry(&ewq->wq, current);
+	userfaultfd_init_waitqueue(ctx, ewq);
 	release_new_ctx = NULL;
 
 	spin_lock(&ctx->event_wqh.lock);
@@ -596,7 +619,7 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 	__add_wait_queue(&ctx->event_wqh, &ewq->wq);
 	for (;;) {
 		set_current_state(TASK_KILLABLE);
-		if (ewq->msg.event == 0)
+		if (READ_ONCE(ewq->waken))
 			break;
 		if (READ_ONCE(ctx->released) ||
 		    fatal_signal_pending(current)) {
@@ -653,9 +676,10 @@ static void userfaultfd_event_wait_completion(struct userfaultfd_ctx *ctx,
 static void userfaultfd_event_complete(struct userfaultfd_ctx *ctx,
 				       struct userfaultfd_wait_queue *ewq)
 {
-	ewq->msg.event = 0;
-	wake_up_locked(&ctx->event_wqh);
-	__remove_wait_queue(&ctx->event_wqh, &ewq->wq);
+	struct userfaultfd_wake_key key = { 0 };
+
+	key.event = ewq->msg.event;
+	 __wake_up_locked_key(&ctx->event_wqh, TASK_NORMAL, &key);
 }
 
 int dup_userfaultfd(struct vm_area_struct *vma, struct list_head *fcs)
@@ -854,8 +878,10 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	struct userfaultfd_ctx *ctx = file->private_data;
 	struct mm_struct *mm = ctx->mm;
 	struct vm_area_struct *vma, *prev;
-	/* len == 0 means wake all */
-	struct userfaultfd_wake_range range = { .len = 0, };
+	/* event == 0 means wake all */
+	struct userfaultfd_wake_key key = {
+		.event = 0,
+	};
 	unsigned long new_flags;
 
 	WRITE_ONCE(ctx->released, true);
@@ -903,12 +929,12 @@ static int userfaultfd_release(struct inode *inode, struct file *file)
 	 * the fault_*wqh.
 	 */
 	spin_lock(&ctx->fault_pending_wqh.lock);
-	__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &range);
-	__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &range);
+	__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL, &key);
+	__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, &key);
 	spin_unlock(&ctx->fault_pending_wqh.lock);
 
 	/* Flush pending events that may still wait on event_wqh */
-	wake_up_all(&ctx->event_wqh);
+	__wake_up(&ctx->event_wqh, TASK_NORMAL, 0, &key);
 
 	wake_up_poll(&ctx->fd_wqh, EPOLLHUP);
 	userfaultfd_ctx_put(ctx);
@@ -1201,20 +1227,20 @@ static ssize_t userfaultfd_read(struct file *file, char __user *buf,
 }
 
 static void __wake_userfault(struct userfaultfd_ctx *ctx,
-			     struct userfaultfd_wake_range *range)
+			     struct userfaultfd_wake_key *key)
 {
 	spin_lock(&ctx->fault_pending_wqh.lock);
 	/* wake all in the range and autoremove */
 	if (waitqueue_active(&ctx->fault_pending_wqh))
 		__wake_up_locked_key(&ctx->fault_pending_wqh, TASK_NORMAL,
-				     range);
+				     key);
 	if (waitqueue_active(&ctx->fault_wqh))
-		__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, range);
+		__wake_up_locked_key(&ctx->fault_wqh, TASK_NORMAL, key);
 	spin_unlock(&ctx->fault_pending_wqh.lock);
 }
 
 static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
-					   struct userfaultfd_wake_range *range)
+					   struct userfaultfd_wake_key *key)
 {
 	unsigned seq;
 	bool need_wakeup;
@@ -1241,7 +1267,7 @@ static __always_inline void wake_userfault(struct userfaultfd_ctx *ctx,
 		cond_resched();
 	} while (read_seqcount_retry(&ctx->refile_seq, seq));
 	if (need_wakeup)
-		__wake_userfault(ctx, range);
+		__wake_userfault(ctx, key);
 }
 
 static __always_inline int validate_range(struct mm_struct *mm,
@@ -1567,10 +1593,11 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
 			 * permanently and it avoids userland to call
 			 * UFFDIO_WAKE explicitly.
 			 */
-			struct userfaultfd_wake_range range;
-			range.start = start;
-			range.len = vma_end - start;
-			wake_userfault(vma->vm_userfaultfd_ctx.ctx, &range);
+			struct userfaultfd_wake_key key;
+			key.event = UFFD_EVENT_PAGEFAULT;
+			key.arg.range.start = start;
+			key.arg.range.len = vma_end - start;
+			wake_userfault(vma->vm_userfaultfd_ctx.ctx, &key);
 		}
 
 		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING | VM_UFFD_WP);
@@ -1622,7 +1649,7 @@ static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
 {
 	int ret;
 	struct uffdio_range uffdio_wake;
-	struct userfaultfd_wake_range range;
+	struct userfaultfd_wake_key key;
 	const void __user *buf = (void __user *)arg;
 
 	ret = -EFAULT;
@@ -1633,16 +1660,17 @@ static int userfaultfd_wake(struct userfaultfd_ctx *ctx,
 	if (ret)
 		goto out;
 
-	range.start = uffdio_wake.start;
-	range.len = uffdio_wake.len;
+	key.event = UFFD_EVENT_PAGEFAULT;
+	key.arg.range.start = uffdio_wake.start;
+	key.arg.range.len = uffdio_wake.len;
 
 	/*
 	 * len == 0 means wake all and we don't want to wake all here,
 	 * so check it again to be sure.
 	 */
-	VM_BUG_ON(!range.len);
+	VM_BUG_ON(!key.arg.range.len);
 
-	wake_userfault(ctx, &range);
+	wake_userfault(ctx, &key);
 	ret = 0;
 
 out:
@@ -1655,7 +1683,7 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 	__s64 ret;
 	struct uffdio_copy uffdio_copy;
 	struct uffdio_copy __user *user_uffdio_copy;
-	struct userfaultfd_wake_range range;
+	struct userfaultfd_wake_key key;
 
 	user_uffdio_copy = (struct uffdio_copy __user *) arg;
 
@@ -1691,12 +1719,13 @@ static int userfaultfd_copy(struct userfaultfd_ctx *ctx,
 		goto out;
 	BUG_ON(!ret);
 	/* len == 0 would wake all */
-	range.len = ret;
+	key.event = UFFD_EVENT_PAGEFAULT;
+	key.arg.range.len = ret;
 	if (!(uffdio_copy.mode & UFFDIO_COPY_MODE_DONTWAKE)) {
-		range.start = uffdio_copy.dst;
-		wake_userfault(ctx, &range);
+		key.arg.range.start = uffdio_copy.dst;
+		wake_userfault(ctx, &key);
 	}
-	ret = range.len == uffdio_copy.len ? 0 : -EAGAIN;
+	ret = key.arg.range.len == uffdio_copy.len ? 0 : -EAGAIN;
 out:
 	return ret;
 }
@@ -1707,7 +1736,7 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
 	__s64 ret;
 	struct uffdio_zeropage uffdio_zeropage;
 	struct uffdio_zeropage __user *user_uffdio_zeropage;
-	struct userfaultfd_wake_range range;
+	struct userfaultfd_wake_key key;
 
 	user_uffdio_zeropage = (struct uffdio_zeropage __user *) arg;
 
@@ -1738,12 +1767,13 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
 		goto out;
 	/* len == 0 would wake all */
 	BUG_ON(!ret);
-	range.len = ret;
+	key.event = UFFD_EVENT_PAGEFAULT;
+	key.arg.range.len = ret;
 	if (!(uffdio_zeropage.mode & UFFDIO_ZEROPAGE_MODE_DONTWAKE)) {
-		range.start = uffdio_zeropage.range.start;
-		wake_userfault(ctx, &range);
+		key.arg.range.start = uffdio_zeropage.range.start;
+		wake_userfault(ctx, &key);
 	}
-	ret = range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
+	ret = key.arg.range.len == uffdio_zeropage.range.len ? 0 : -EAGAIN;
 out:
 	return ret;
 }
-- 
2.7.4